1. Field of the Invention
This invention relates to a process for preparing an optically active aminoalcohol derivative useful as a production intermediate for medicines, agricultural agents and so forth; for example, a process for preparing erythro-(1R,2S)-p-hydroxynorephedrine. This invention also relates to an optically active 5-hydroxyoxazolidine derivative as an important intermediate for production of the above optically active aminoalcohol derivative or a number of other optically active amine derivatives as well as a preparing process therefor. For example, an optically active 5-hydroxyoxazolidine derivative according to this invention is also very useful as a production intermediate for an azole antibacterial agent. A compound defined by general formula (1), (3) or (4) which has an asymmetric carbon having R1 and an amino substituent represents a R— or S-form, but not a racemic mixture of the R and S forms. A compound defined by general formula (5) or (6) having two adjacent asymmetric carbons which have an amino and hydroxy substituents represents a R—S or S—R form, but not an R—R or S—S form.
2. Description of the Prior Art
Recently, optically active compounds have been increasingly needed in many applications including medicines and agricultural agents. For industrial applications, there has been strongly needed for a convenient and inexpensive process for preparing an optically active material.
The following three processes are those according to the prior art for preparing an optically active aminoalcohol derivative relating to this invention:
[1] A method, in which, after a racemic compound of the desired compound is chemically synthesized, it is then optically resolved via, for example, a diastereomer salt to give the desired optically active compound. [2] A method, in which a technique for chemical or biological asymmetric synthesis is employed to give an optically active compound from an optically inactive material.
[3] A method by a so-called “chiral pool method”, in which it starts from an optically active material and the optical active compound is obtained under prevention of racemization.
Regarding the process in [1] as “A method, in which, after a racemic compound of the desired compound is chemically synthesized, it is then optically resolved via, for example, a diastereomer salt to give the desired optically active compound”, an example may be a process according to the prior art for preparing erythro-(1R,2S)-p-hydroxynorephedrine within a category of desired optically active aminoalcohol derivatives in this invention, in which after a racemate having the desired structure is first chemically synthesized, its optical resolution is carried out using an optically active carboxylic acid such as D-tartaric acid (J. Med. Chem., 1977, 20, 7, 978).
However, as long as using a preparation process on the basis of optical resolution, it is theoretically impossible to increase the yield over 50%, unless an enantiomer is recovered and subject to a special treatment such as racemization. Furthermore, an optically active carboxylic acid and the other compounds required in resolution are generally expensive, and it is often necessary to repeat several times a process such as recrystallization. In other words, the optical resolution process requires an expensive resolving agent(s) and a multiple-stage operation, and is, therefore, industrially a high-cost preparation process.
The process in [2] as “A method, in which a technique for chemical or biological asymmetric synthesis is employed to give an optically active compound from an optically inactive material” has been significantly advanced. As examples, there are mentioned an asymmetric synthesis technique based on a chemical synthesis including the uses of asymmetric reduction catalysts or the other agents (J. Am. Chem. Soc., 1980, 102, 7932) and an asymmetric synthesis technique based on a biotechnological synthesis using an enzyme or the other agents (Japanese Patent Laid-open No. 62-29998). Unfortunately, specificity for each substrate is significantly involved in practical production and thus the process cannot be applied to all kinds of production. Furthermore, the process cannot be always inexpensive when requiring an expensive asymmetric catalyst. In practice, for an optically active aminoalcohol derivative as a desired compound in this invention, there has been available no industrially reasonable preparation processes on the basis of chemical or biotechnological technique as described above.
For the process in [3] as “A method by a so-called “chiral pool method”, in which it starts from an optically active material and the optical active compound is obtained under prevention of racemization”, there have been many problems to be solved; for example, control of racemization is difficult till now and furthermore, practical production requires multiple steps. Regarding the aminoalcohol derivatives as the desired compounds in the present invention, no processes have been reported till now, which is fully satisfactory in the industrial viewpoint.
Regarding the prior art techniques for production of the optically active aminoalcohol derivatives, only the processes, which are difficult in the industrial viewpoint and require considerably high cost. Therefore, a novel, inexpensive and more convenient processes for the production are strongly desired.
Furthermore, only the following processes [4] to [6] are known in the prior art for preparation of an optically active 5-hydroxyoxazolidine derivative as an important production intermediate in the process of this invention:
[4] A method, in which (4S)-N-(ethoxycarbonyl)-4-(2-phenylethyl)-5-oxazolidinone is reacted with 4-chloro-3-methoxyphenyl magnesium bromide (WO 95/09155).
[5] A method, in which a 5-oxazolidinone derivative is reacted with a halomethyl lithium (WO 00/53571).
[6] A method, in which a 5-oxazolidinone derivative is reacted with (trifluoromethyl)trimethylsilane (J. Org. Chem. 1998, 63 (15), 5179).
In the above [4], the compound as a starting material is a special synthetic, non-naturally, compound relating to amino-acids, which has a phenylethyl group in its side chain. The compound is, therefore, prepared by a multistep reaction and it is difficult to obtain the compound in general. In addition, it is not an inexpensive material in the viewpoint of its production cost and the process maintains a significant problem in raw material supply. Furthermore, in the above process [4], the process is extremely limited, as a single production example, to that of the compound having a 4-chloro-3-methoxyphenyl group at 5-position in the oxazolidinone ring as a principal structure, and the product is used only as a starting material for a limited application to produce a medicine (Sch39166). It cannot be said that the preparation process as an example described in [4] is a universal process, and that, regarding an optically active 5-hydroxyoxazolidine derivative, which is widely useful, its preparation process has been fully established.
Regarding the compounds described in above [5] or [6], a special functional group such as a haloalkyl group (for example, a chloromethyl group) and a trifluoromethyl group is reacted at the 5-position of the oxazolidine as a main structure, but neither aryl nor hetero ring, which are widely useful for an intermediate of a medicine and agricultural agent are not included.
Although an optically active aminoalcohol derivative having an aryl group or heterocycle has been increasingly demanded in many applications such as in the pharmaceutical and agricultural fields, no general production methods has been found in the prior art, regarding the optically active 5-hydroxyoxazolidine derivative having an aryl group or heterocycle at the 5-position as its important production intermediate.
As a known prior art for preparation of an optically active aminoketone relating to this invention, a process is known, which uses a reaction where a carboxyl group in an N-protected amino acid is converted into an acid chloride, which then undergoes Friedel-Crafts reaction (J. Am. Chem. Soc. 1981, 103, 6157). Acylation using Friedel-Crafts reaction is, however, not considered to be a general preparation method for the reasons that the reaction causes racemization, that the reaction is considerably restricted by a structure to be acylated and that sometimes an aminoketone produced cannot be isolated. Thus, an industrially practical process is needed.